My chickens are about 2 years old and recently 2 out of 16 have started loosing feathers off the butt area and their feathers overall look poor. I have looked for the actual mite or lice but I don't see anything. However, I'm not sure what to look for. Does anyone have any advice about what to look or what might be causing this? They molted over the fall/winter. I was going to take a stool sample in to be analyzed for worms. Any help would be appreciated.